Electrochemical immunosensors based on single-wall CNT forest platforms with multi-label secondary antibody nanotube bioconjugates have been reported as highly sensitive detection platform. (Xin et al. “Carbon Nanotube Amplification Strategies for Highly Sensitive Immunodetection of Cancer Biomarkers”, Journal of the American Chemical Society 2006 128 (34), pp 11199-11205, incorporated by reference herein). In this case, the SWNT forest was standing in upright bundles on Nafion-iron oxide decorate conductive surface. Amplified sensitivity was achieved by using bioconjugates featuring horseradish peroxidase (HRP) labels and secondary antibodies (Ab2) linked to multiwall CNT at high HRP-to-Ab2 ratio to replace singly labeled secondary antibodies. Due to the complexity of fabrication process for the CNT forest, an alternative platform using densely packed AuNPs was recently reported. (Vigneshwaran Mani et al. “Ultrasensitive Immunosensor for Cancer Biomarker Proteins Using Gold Nanoparticle Film Electrodes and Multienzyme-Particle Amplification”, ACS Nano Letters, 2009, 3 (3), pp 585-594, incorporated by reference herein). In the study, HRP labels were attached to carboxyl groups created on the magnetic bead surface to improve the sensitivity and detection limit. After the bioconjugation of HRP and Ab2, the free antibodies and HRP were easily separated from the Ab2 magnetic bead-HRP by using a magnet to localize the beads at the bottom of a test tube and washing to remove unreacted protein. Magnetic particles for medical applications have been developed. Since magnetic particles have unique magnetic features not present in other materials, they can be applied to special medical techniques. See, e.g., Choi, J-W et al. “An integrated microfluidic biochemical detection system with magnetic bead-based sampling and analysis capabilities.” Electrochemistry Communications. 2001, 9, pp 1547-1552. and R. E. Thilwind, et al. “Measurement of the concentration of magnetic nanoparticles in a fluid using a giant magnetoresistance sensor with a trench.” J. Magnetism and Magnetic Materials, 2008, 320, pp 486-489, both incorporated by reference herein.
Separation, immunoassay, magnetic resonance imaging (MRI), drug delivery, and hyperthermia are enhanced by the use of magnetic particles. An example of magnetic particles used in biodetection to enable point-of-care diagnostics was recently demonstrated by Philips' Magnotech handheld technology. Integrated into a disposable biosensor cartridge that inserts into a hand-held analyzer, Magnotech uses magnetic nanoparticles to measure target molecules in picomolar concentrations in just a few minutes. Furthermore, the technology improves ease of use by simplifying fluidic washing steps. Although magnetic beads have been used in various biodetection applications, they often involve complex surface functionalization. The conformity and stability of the surface coating can affect toxicity and robustness of bindings.